Metal-organic frameworks with precisely designed interior for carbon dioxide capture in the presence of water

Article abstract of DOI:10.1021/ja503296c

The selective capture of carbon dioxide in the presence of water is an outstanding challenge. Here, we show that the interior of IRMOF-74-III can be covalently functionalized with primary amine (IRMOF-74-III-CH₂NH ₂) and used for the selective capture of CO₂ in 65% relative humidity. This study encompasses the synthesis, structural characterization, gas adsorption, and CO₂ capture properties of variously functionalized IRMOF-74-III compounds (IRMOF-74-III-CH₃, -NH₂, -CH₂NHBoc, -CH₂NMeBoc, -CH ₂NH₂, and -CH₂NHMe). Cross-polarization magic angle spinning ¹³C NMR spectra showed that CO₂ binds chemically to IRMOF-74-III-CH₂NH₂ and -CH₂NHMe to make carbamic species. Carbon dioxide isotherms and breakthrough experiments show that IRMOF-74-III-CH₂NH₂ is especially efficient at taking up CO₂ (3.2 mmol of CO₂ per gram at 800 Torr) and, more significantly, removing CO₂ from wet nitrogen gas streams with breakthrough time of 610 ± 10 s g^-1 and full preservation of the IRMOF structure.

Full text of DOI:10.1021/ja503296c

Communication
pubs.acs.org/JACS
Metal−Organic Frameworks with Precisely Designed Interior for
Carbon Dioxide Capture in the Presence of Water
Alejandro M. Fracaroli,† Hiroyasu Furukawa,† Mitsuharu Suzuki,† Matthew Dodd,§ Satoshi Okajima,†
Felipe Gandara,† Jeffrey A. Reimer,§ and Omar M. Yaghi*,†,‡
́
†Department of Chemistry, University of CaliforniaBerkeley, Materials Sciences Division, Lawrence Berkeley National Laboratory,
and Kavli Energy NanoSciences Institute at Berkeley, Berkeley, California 94720, United States
‡King Fahd University of Petroleum and Minerals, Dhahran 34464, Saudi Arabia
§Department of Chemical and Biomolecular Engineering, University of CaliforniaBerkeley, and Environmental Energy
Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
S
* Supporting Information
class of materials for this application has yet to emerge.
ABSTRACT: The selective capture of carbon dioxide in
the presence of water is an outstanding challenge. Here, we
show that the interior of IRMOF-74-III can be covalently
functionalized with primary amine (IRMOF-74-III-
CH2NH2) and used for the selective capture of CO2 in
65% relative humidity. This study encompasses the
synthesis, structural characterization, gas adsorption, and
CO2 capture properties of variously functionalized
IRMOF-74-III compounds (IRMOF-74-III-CH3, -NH2,
-CH2 NHBoc, -CH2 NMeBoc, -CH2 NH2 , and
-CH2NHMe). Cross-polarization magic angle spinning
13C NMR spectra showed that CO2 binds chemically to
IRMOF-74-III-CH2NH2 and -CH2NHMe to make
carbamic species. Carbon dioxide isotherms and break-
through experiments show that IRMOF-74-III-CH2NH2 is
especially efficient at taking up CO2 (3.2 mmol of CO2 per
gram at 800 Torr) and, more significantly, removing CO2
from wet nitrogen gas streams with breakthrough time of
Although carbon capture in mesoporous materials and carbon
has been shown under humid conditions,4c MOFs show special
promise because of their adjustable chemical functionality,
structural diversity, and ease of functionalization.6 Capture of
CO2 from dry gas mixtures (nitrogen, methane, and oxygen)
has been reported in MOFs incorporating amines bound to
either metal sites7 or organic linkers.8 However, successful
demonstrations of MOFs capable of CO2 capture in the
presence of water, and doing so without degradation of
performance as a result of competition with water, remain
uncommon.4b
In this Communication, we show how the interior of porous
MOFs can be designed to overcome the complications
presented by the competition of water with CO2. We chose a
MOF constructed from magnesium oxide rods joined by
terphenylene organic linkers {IRMOF-74-III,
Mg2(DH3PhDC), where H4DH3PhDC = 2′,5′-dimethyl-3,3″-
dihydroxy-[1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid, Figure
1} to make an extended structure with an etb topology
supporting one-dimensional channels of 25 Å in their diagonal.9
The organic linkers and their corresponding IRMOF-74-III
structures were functionalized with -CH3, -NH2, -CH2NHBoc,
-CH2NMeBoc, -CH2NH2, and -CH2NHMe (Boc = tert-
butyloxycarbonyl), which point toward the center of the
channels (Figure 1). Here, we report the synthesis, character-
ization, porosity, and CO2 capture properties (in dry and wet
nitrogen streams) of IRMOF-74-III with the six different
functionalities, vide supra. We find that at low pressure IRMOF-
74-III-CH2NH2 and -CH2NHMe exhibit strong binding of CO2
and have the highest uptake, and that in breakthrough
experiments the -CH2NH2 form shows selectivity toward
CO2 in a wet nitrogen gas stream with 65% relative humidity
(RH). Indeed, the behavior of this material under wet
conditions remains unchanged from that observed under dry
gas stream.
610
structure.
10 s g−1 and full preservation of the IRMOF
arbon dioxide capture from combustion sources such as
flue gas in power plants is an outstanding challenge
C
because CO2 has to be selectively removed from other gases
and, most importantly, water.1 Porous materials can trap CO2
in voluminous amounts, but when water is present the
efficiency of capture is significantly reduced, as water competes
for the binding sites within the pores.2 Aqueous monoethanol-
amine (MEA) solutions are efficient at binding CO2; however,
they present a major energy cost and environmental hazard.3
Thus, a need exists to develop materials capable of addressing
this carbon capture challenge.
The preferred method for measuring the efficiency of a given
material for capture of CO2 is to expose a solid form of the
material to a mixture of gases containing CO2 and water, and
then to detect the gases and measure the time they take to pass
through the material (breakthrough time).4 Various porous
materials5 such as zeolites, mesoporous silica, polymeric resins,
porous carbon, and metal−organic frameworks (MOFs) are
being studied for their CO2 capture properties, but a viable
The synthesis of the appropriate linkers for IRMOF-74-III
compounds is shown in Figure 1. Starting from the
commercially available methyl 2-hydroxy-4-iodobenzoate (1),
Received: April 2, 2014
© XXXX American Chemical Society
A
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Figure 1. Synthetic pathway for the functionalized organic linkers used in the synthesis of IRMOF-74-III. This methodology allowed us to prepare
-CH3 (5a), -NH2, (5b), -CH2NHBoc (5c), and -CH2NMeBoc (5d) functionalized linkers. On the right is shown a schematic representation of the
IRMOF-74-III pore as functionalized with the organic linkers 5a−5d and post-synthetic deprotection of Boc groups. Color code: C in gray, O in red,
functional groups in purple, Mg as blue polyhedra.
we synthesized four different organic linkers by using Suzuki−
Miyaura coupling of boronic acid pinacol ester (2) and
functionalized 1,4-dibromobenzenes (3), followed by saponifi-
cation reaction of the methyl ester linker derivatives (4a−4d).
The synthetic method was designed to achieve versatility in the
covalent incorporation of a variety of functional groups within
the pores of IRMOF-74-III. The linkers 5a−5d have -CH3,
-NH2, -CH2NHBoc, and -CH2NMeBoc functional groups,
respectively. We have employed the Boc protecting group in
order to introduce -CH2NH2 and -CH2NHMe into IRMOF-
74-III, as the unprotected amines may react with the metal ions
used for the MOF structure synthesis. The synthesized linkers
were fully characterized by nuclear magnetic resonance (1H and
13C NMR) and electrospray ionization mass spectrometry (ESI-
MS), and single-crystal X-ray diffraction (XRD) in the case of
-NH2 and -CH2NMeBoc linkers [section S1, Supporting
Information (SI)].
Four IRMOF-74-III structures incorporating 5a−5d were
prepared according to reported conditions.9 The synthesis of
IRMOF-74-III-CH2NHBoc is typical: a solvent mixture
containing Mg(NO3)2·6H2O (160 mg, 0.62 mmol), linker 5c
(90 mg, 0.19 mmol), and 15 mL of N,N-dimethylformamide
(DMF)/ethanol/water (9:0.5:0.5) was placed in a 20 mL
capped vial, which was heated at 120 °C for 20 h. Depending
on the functionality incorporated in the interior of the MOF,
white (-CH3), yellow (-NH2), or pale yellow (-CH2NHBoc and
-CH2NMeBoc) microcrystalline solids were obtained (Figure
S3).
The Boc protecting groups in IRMOF-74-III-CH2NHBoc
and -CH2NMeBoc were removed using a modification of a
reported post-synthetic deprotection procedure.10 In our case,
microwave heating was applied (230 °C) for 10 min in a
ternary mixture of solvents [2-ethyl-1-hexanol/ethylene glycol/
water (9.1:0.5:0.5)]. This process allowed us to quantitatively
obtain the unprotected primary (-CH2NH2) and secondary
amine (-CH2NHMe) groups in the interior of those MOFs.
The successful deprotection was examined by solution 1H
NMR spectra of the digested samples in 50 mM DCl in a
DMSO-d6/D2O mixture, where the absence of the correspond-
ing Boc group resonance peaks at δ = 1.35 ppm and δ = 1.28
ppm was confirmed for IRMOF-74-III-CH2NH2 and
-CH2NHMe, respectively. Similar NMR analysis was carried
out for the remaining IRMOF-74-III structures and confirmed
the presence of the appropriate functionality (section S4, SI).
To evaluate the porosity and crystallinity of these materials,
as-synthesized samples were activated by immersion in 10 mL
of DMF for 4 h, the liquid was decanted, and then the process
was repeated three times per day for 3 days. This whole
protocol was repeated with methanol during 3 additional days
to obtain the solid with washed interior. The solvent within the
pores of the resulting solids was removed under dynamic
vacuum initially at room temperature and then by heating at
120 °C for 12 h. The crystallinity and structure of the evacuated
series of IRMOF-74-III compounds were confirmed by the
coincidence of the sharp powder X-ray diffraction (PXRD)
lines with those of the parent unfunctionalized IRMOF-74-III
(section S5, SI). In addition, PXRD analysis of the IRMOF-74-
III-CH2NH2 and -CH2NHMe samples further confirmed that
the frameworks maintain their structural integrity and porosity
after post-synthetic deprotection of the Boc groups. Nitrogen
adsorption isotherms were measured at 77 K, and the
Brunauer−Emmett−Teller (BET) surface areas were calculated
to be 2640, 2720, 2170, 2220, 2310, and 2250 m2 g−1 for
IRMOF-74-III-CH3, -NH2, -CH2NHBoc, -CH2NMeBoc,
-CH2NH2, and -CH2NHMe, respectively. These values are
similar to the BET surface area of the parent IRMOF-74-III
(2440 m2 g−1),9 indicating that porosity is maintained in the
functionalized as well as the deprotected forms.
The CO2 uptake capacity for each of the functionalized
IRMOF-74-III compounds was obtained by measuring the
corresponding isotherms at 25 °C (Figure 2a). All the
compounds showed significant CO2 uptake, and, as expected,
IRMOF-74-III-CH3, -NH2, -CH2NH2, and -CH2NHMe exhibit
similar capacity at 800 Torr, while the protected compounds
IRMOF-74-III-CH2NHBoc and -CH2NMeBoc showed lesser
uptake because of the sterically bulky Boc groups (Figure 2a).
Interestingly, IRMOF-74-III-CH2NH2 and -CH2NHMe
showed the highest uptake capacities at low CO2 pressure
range (<1 Torr, Figure 2b) with hysteresis, retaining ca. 20 cm3
g−1 of CO2 upon desorption down to 10 Torr (Figure 2a). This
trend can be attributed to the strong interactions between CO2
and aliphatic amine functionalities. A second CO2 isotherm was
recorded after evacuation of the sample at room temperature
for 2 h (second cycle, Figure 2c). As expected, the initial slope
of the CO2 uptake in the second cycle for IRMOF-74-III-
CH2NH2 and -CH2NHMe was 1/3.6 and 1/4.6 compared to
the first cycle, and the maximum uptakes at 800 Torr were less
than those of the first cycles (by ca. 18 and 15 cm3 g−1 for
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Communication
-CH2NHBoc samples, this peak is absent (Figure S18). This
difference in the 13C NMR spectra confirms that CO2 is only
chemisorbed by -CH2NH2 and -CH2NHMe amine-function-
alized IRMOF-74-III, but not by MOFs with -NH2 and
-CH2NHBoc functionalities.
Given the fully reversible nature of the CO2 uptake of
IRMOF-74-III-CH2NH2 (Figure 2c), we carried out a dynamic
separation experiment to evaluate the breakthrough time in the
absence and presence of water. Here, a solid sample of IRMOF-
74-III-CH2NH2 compound (238 mg, 0.56 mmol) was packed
in a 10 cm length × 0.6 cm diameter stainless steel column and
utilized as an adsorbent bed. A mixed gas containing 16% (v/v)
of CO2 in a nitrogen gas stream was introduced to the column,
and the effluent was monitored by a mass spectrometer.4 The
breakthrough time was determined when the CO2 concen-
tration in the effluent reached 5% of the influent concentration.
Under dry conditions, the IRMOF-74-III-CH2NH2 adsorb-
ent bed held CO2 up to 670 10 s g−1, which is equivalent to a
kinetic CO2 adsorption capacity of 0.8 mmol g−1. The CO2
influent was then stopped and, to regenerate the material, we
purged the adsorbent bed with dry nitrogen; however, this was
not enough to fully remove adsorbed CO2 (Figure 3a).
Therefore, the sample bed was heated at 95 °C under nitrogen
flow for 30 min, upon which appearance of CO2 signal on the
mass spectrometer indicated the liberation of chemically bound
CO2. The amount of released CO2 was calculated by
integration of the peak area and found to be 50% of the total
uptake capacity of the MOF under these conditions. The
regenerated IRMOF-74-III-CH2NH2 showed a breakthrough
time as long as the one for the first run (Figure S19). This
indicates that amine functionalities incorporated into the
IRMOF-74-III require moderate regeneration conditions
compared to MEA (ca. 120 °C) and other amine-functionalized
MOFs.7a As a control experiment, we subjected IRMOF-74-III-
CH3 under the same conditions used for IRMOF-74-III-
CH2NH2 and found a longer breakthrough time (1380 10 s
g−1);12 however, upon purging the sample with nitrogen, all
adsorbed CO2 was recovered, indicating, as expected, no
carbamate formation (Figure S20).
Figure 2. (a) Comparison of CO2 uptake at 25 °C for IRMOF-74-III-
CH3 (gray), -NH2 (green), CH2NH2 (red), -CH2NHMe (blue),
-CH2NHBoc (purple), and -CH2NMeBoc (cyan). (b) Expansion of
the low pressure range (>1 Torr). Carbon dioxide isotherms at 25 °C
for IRMOF-74-III-CH2NH2 (c) and -CH2NHMe (d). Uptakes for
samples after activation (first cycle), after first CO2 uptake (second
cycle), and after 120 °C heating for 1 h for regeneration (third cycle)
are shown in circles, triangles, and squares, respectively.
IRMOF-74-III-CH2NH2 and -CH2NHMe, respectively). As
this evidence clearly indicated a strongly bound CO2, the solids
were heated to 120 °C under vacuum (10 mTorr) for 1 h, and
isotherms for the third cycle of CO2 uptake were measured. In
the case of IRMOF-74-III-CH2NH2, the CO2 was fully
desorbed, while partial desorption was observed for IRMOF-
74-III-CH2NHMe (third cycle, Figure 2c,d).
Cross-polarization magic angle spinning 13C NMR spectra
were collected for each of IRMOF-74-III-NH2, -CH2NHBoc,
-CH2NH2, and -CH2NHMe to evaluate the possibility of
carbamate formation, which would be expected in the reaction
of CO2 with IRMOF-74-III-CH2NH2 and -CH2NHMe and not
the others. Activated samples of these MOFs were exposed to
13C-labeled CO2 at room temperature and ca. 760 Torr for 24 h
before the samples were transferred into a solid-state NMR
rotor. The 13C NMR spectra of IRMOF-74-III-CH2NH2 and
-CH2NHMe show a broad resonance peak centered at δ = 160
ppm, corresponding to the chemical shift of carbamate species
resonance (carbamate ions and carbamic acid) reported in the
literature,4a,11 while in the case of IRMOF-74-III-NH2 and
Both IRMOF-74-III-CH2NH2 and -CH3 were examined by
similar breakthrough experiments, but now in the presence of
water. Prior to the breakthrough measurements, wet nitrogen
with 65% RH was introduced to the adsorbent bed until the
water concentration of the effluent showed a constant value
(>16 h). To estimate the breakthrough time in the presence of
water, we introduced a gas mixture containing 16% of dry CO2
Figure 3. (a) IRMOF-74-III-CH2NH2 breakthrough cycle under dry conditions. Breakthrough time is highlighted in light blue. (b) Breakthrough
curves for IRMOF-74-III-CH3 under dry conditions (gray empty markers) and wet conditions (gray filled markers), and for IRMOF-74-III-CH2NH2
under dry conditions (red empty markers) and in the presence of water (red filled markers).
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Schuth, F.; Bongard, H.-J.; Lu, A.-H. J. Am. Chem. Soc. 2011, 133,
11378.
̈
and 84% of wet nitrogen (65% RH). IRMOF-74-III-CH2NH2
showed a breakthrough time nearly identical to that observed
under dry conditions (610 10 s g−1) (Figure 3b), while the
breakthrough time of IRMOF-74-III-CH3 under wet conditions
showed an 80% decrease compared to that in the absence of
moisture. This behavior indicates that the CO2 uptake in
IRMOF-74-III-CH3 is, as expected, mainly attributable to the
open magnesium sites, which are occupied by water molecules
under humid conditions.12 In IRMOF-74-III-CH2NH2, the
CO2 uptake takes place at the linker amine sites, while the open
magnesium sites are not accessible under dry nor humid
conditions (section S7, SI); therefore, the effect of water on the
CO2 uptake should be negligible. This is also supported by the
dissimilar desorption behavior compared to IRMOF-74-III-
CH3 (Figures 3a and S20).
IRMOF-74-III-CH2NH2 with bound CO2 was regenerated
by purging with dry nitrogen followed by heating at 90 °C to
remove the CO2. A second cycle of humidification and CO2
uptake was applied as explained above to obtain a nearly
identical breakthrough time (600 10 s g−1) (section S9, SI).
We further note that the PXRD pattern of the sample after
these cycles was identical to that of the activated sample, thus
indicating full preservation of IRMOF-74-III-CH2NH2 struc-
ture throughout the CO2 capture process (Figure S16).
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ASSOCIATED CONTENT
* Supporting Information
■
S
Detailed organic linkers and MOFs synthetic procedures,
including characterization by NMR spectra, PXRD, nitrogen
adsorption, breakthrough experiments, and complete refs 4b,
5g, and 9. This material is available free of charge via the
Internet at http://pubs.acs.org.
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H.-C. Angew. Chem., Int. Ed. 2012, 51, 7480. (b) Arstad, B.; Fjellvag,
̊
H.; Kongshaug, K. O.; Swang, O.; Blom, R. Adsorption 2008, 14, 755.
(c) Qiao, Z.; Zhou, J.; Lu, X. Fluid Phase Equilib. 2014, 362, 342.
(9) Deng, H.; et al. Science 2012, 336, 1018.
AUTHOR INFORMATION
Corresponding Author
yaghi@berkeley.edu
■
(10) (a) Cohen, S. M. Chem. Rev. 2012, 112, 970. (b) Lun, D. J.;
Waterhouse, G. I. N.; Telfer, S. G. J. Am. Chem. Soc. 2011, 133, 5806.
(11) Pinto, M. L.; Mafra, L.; Guil, J. M.; Pires, J.; Rocha, J. Chem.
Mater. 2011, 23, 1387.
Notes
The authors declare no competing financial interest.
(12) Liu, J.; Benin, A. I.; Furtado, A. M. B.; Jakubczak, P.; Willis, R.
ACKNOWLEDGMENTS
R.; LeVan, M. D. Langmuir 2011, 27, 11451.
■
This work was partially supported for synthesis and character-
ization by BASF SE (Ludwigshafen, Germany), gas adsorption
by U.S. Department of Defense, Defense Threat Reduction
Agency (HDTRA 1-12-1-0053), and carbon dioxide adsorption
studies by the U.S. Department of Energy, Office of Science,
Office of Basic Energy Sciences, Energy Frontier Research
Center (DE-SC0001015).
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